Pulsed detonation engine

ABSTRACT

The invention relates to a pulsed detonation engine. According to the invention, the transversal base ( 3 ) or the flame tube ( 2 ) is mounted in such a way that it can move in relation to said tube in order to be able to assume two boundary positions, first position corresponding to the detonation phase of the combustible charge in the combustion chamber ( 5 ) of the tube, and a second position corresponding to the phase wherein the combustible charge is supplied to said chamber. At least one supply opening ( 7 ) for the combustible charge is provided in the lateral wall ( 4 ) of the tube, said opening being closed and separated from the combustion chamber ( 5 ) when the mobile base ( 3 ) assumes the first position thereof, and communicating with the chamber ( 5 ) in a fluidic manner when the mobile base ( 3 ) assumes the second position thereof.

The present invention relates to a pulsed detonation engine, that is tosay a reciprocating internal combustion engine using a supersoniccombustion mode (detonation) which makes it possible to deliver veryhigh propagation speeds.

This type of engine is applicable especially, although not exclusively,in the aeronautical, space and military fields for equipping aircraft,rockets, missiles, etc.

It is known that detonation is a particular method of propagating aflame which results from the coupling between a shock wave and acombustion front, with the result that the shock wave compresses thecombustible charge (fuel/oxidizer mixture) situated in the combustionchamber of the engine, in order to bring it above its self-ignitiontemperature, and the energy released by the combustion in turn ensuresthe continuity of the shock wave. The operating cycle of such an enginecan thus be reduced to three stages:

-   -   a first stage relating to the supply phase wherein the        combustible charge or mixture is supplied;    -   a second stage relating to the detonation phase in which the        chemical energy generated by the charge is compressed and        released; and    -   a third stage relating to the expansion phase of the detonation        products.

Structurally, the combustion chamber of such an engine is defined by aflame tube closed at one end by a transverse base (termed thrust wall)against which the products from the detonation of the combustible chargepress in order to generate the thrust, which charge is introduced intothe chamber by a supply device.

It is quite obvious that the course of the various phases of the engineoperating cycle is a potentially critical point, it being particularlyimportant to have control over the supply phase, which can have a verygreat influence on the performance of such an engine.

Currently, two injection-supply control devices are mainly used: namelyan aeroacoustic device which uses the overpressure in the chamber toblock the admission of the combustible charge aerodynamically, and anelectromechanical device using a controlled valve which is either of theconventional, translationally movable type or of the rotary type.

Although these supply devices are widely used, they nevertheless havedisadvantages. Specifically, the aeroacoustic device depends on theinjection conditions for the combustible mixture and, even though it isvery simple to produce, it does not allow admission optimization for thewhole range of operation of the engine, which leads to a reduction inthe performance thereof. With regard to the electromechanical device, itrequires conventional valves capable of passing through highinstantaneous flow rates, therefore making these valves expensive, orrotary valves which, although well suited for rocket mode, are lessefficient for aerobic operation. Furthermore, these two types of valvesgreatly complicate the design of the engine, the simplicity of whoseconstruction remains one of the strong points.

The present invention has the aim of overcoming these disadvantages andrelates to a pulsed detonation engine whose design is structurallysimple and guarantees a high degree of operational safety.

To this end, the pulsed detonation engine supplied cyclically with acombustible charge fed into the combustion chamber of a flame tube witha transverse base by a supply device is noteworthy:

-   -   in that said transverse base of the flame tube is mounted so        that it can move with respect to the latter in order to be able        to occupy two boundary positions, a first position corresponding        to the detonation phase of the combustible charge in the        combustion chamber of said tube and a second position        corresponding to the phase wherein the combustible charge is        supplied to said chamber;    -   in that at least one supply opening for said combustible charge        is provided in the lateral wall of said tube, this opening being        closed off and separated from said combustion chamber by said        movable base when the latter is occupying its first position and        being in fluid communication with said chamber when said movable        base is occupying its second position; and    -   in that, in said first position, said transverse movable base is        secured to said tube by releasable locking means.

Thus, by virtue of the invention, the engine dispenses with complexsupply devices having valves or the like, since it is the transversebase itself, forming the thrust wall, which, by being able to move andthereby open and close the supply opening, dictates the operation ofboth the supply and detonation phases of the engine. Consequently, bycontrolling and ensuring correct operation of both these phases andtheir transitions, the movable base may be considered as forming anintegral part of the supply device.

It will also be noted that the use of the transverse movable base forthe autonomous control of the fuel/oxidizer admission into thecombustion chamber is mechanically very simple, guaranteeing high levelsof operational safety and reliability without, moreover, external energyhaving to be supplied.

For example, said transverse movable base may slide with respect to saidtube between said two positions and/or it may rotate with respect tosaid tube between the two positions.

Said transverse base may advantageously take the form of a piston with atransverse wall facing said chamber and with a lateral skirt cooperatingwith the wall of said tube in order to close off said supply opening inthe first position of said base, and said releasable locking means thencomprise an internal block housed in said piston in a sliding manner andpassing through its transverse wall so as to emerge in said combustionchamber, and also at least one locking roller subjected to the movementof said block and being able to pass radially through the lateral skirtof said piston in order to engage in a reception housing of said tubeand to immobilize said base.

As a variant, said transverse movable base may be mounted rotationallyon a piston arranged in said flame tube and be provided with peripherallocking tenons which are able to cooperate, in said first position, withlocking housings which are made in said flame tube and are incommunication with said combustion chamber, and, through the effect of adetonation, said transverse movable base can rotate with respect to saidpiston, inhibiting the cooperation of the locking tenons and the lockinghousings and enabling said piston to assume said second position.

Moreover, an internal stop is provided in said tube in order to mark thefirst position of said movable base. Preferably, said internal stoptakes the form of an internal annular shoulder emanating from thelateral wall of said tube and against which the piston of said movablebase is applied in its first position.

According to another characteristic, elastic return means are providedin said tube in order to return said movable base from its secondposition toward its first position. These elastic return means comprise,for example, at least one spring acting on the internal block of saidmovable base.

Moreover, said lateral supply opening is preferably disposed adjacentlyto said internal stop.

Moreover, the engine may comprise an ignition device which,advantageously, uses the reciprocating movement of said transversemovable base for cyclically igniting the combustible charge.

In a preferred, although not exclusive, embodiment, said ignition deviceis of the piezoelectric type and comprises, for example, a movableweight connected to said transverse movable base, a retaining devicewhich is able to maintain said weight in the primed position, an elasticelement for returning said weight to the percussion position subsequentto the release of said retaining device, and a piezoelectric membergenerating an electrical current in order to ignite said combustiblecharge when said weight comes into the percussion position.

The figures of the attached drawing will make it clear to understand howthe invention can be implemented. In these figures, identical referencesdenote similar elements.

FIG. 1 is a schematic view in longitudinal section of a first exemplaryembodiment of the pulsed detonation engine according to the invention,showing the movable base in the first position.

FIG. 2 is a similar view to the previous one, showing the movable baseof said engine in its second position.

FIG. 3 shows schematically, in section and perspective, the inside ofthe flame tube of a second exemplary embodiment of the presentinvention.

FIGS. 4 and 5 show, schematically and respectively, the first and secondpositions of the transverse movable base of the flame tube of FIG. 3.

FIG. 6 is a schematic view of an ignition device of said engine, inwhich two half-sections, one lower and one upper, are used to representits two end operating positions.

The pulsed detonation engine I, represented schematically and partiallyin FIGS. 1 and 2, comprises a cylindrical flame tube 2 with alongitudinal axis A, and a transverse base 3 housed, with a close fit,inside the flame tube 2. This transverse base 3 delimits, together withthe lateral wall 4 of the tube 2, a combustion chamber 5 (illustrated inpart) which is able to cyclically receive a combustible charge obtainedfrom a supply device (denoted by a rectangle and referenced 6) whichsupplies the fuel/oxidizer mixture. The transverse base 3 defines thethrust wall against which the detonation products of the combustiblecharge are applied in order to generate the thrust.

According to the invention, the transverse base 3 is mounted so that itcan move with respect to the flame tube 2 of the engine I and is able tomove between two distinct boundary positions, a first position (FIG. 1)isolating the combustion chamber 5 from the supply device 6,corresponding to the detonation phase of the combustible charge, and asecond position (FIG. 2) placing the supply device and the combustionchamber in fluid communication, corresponding to the supply phasewherein the chamber is supplied with the combustible charge.

To make this possible, openings 7 for admitting the combustible chargefrom the supply device 6 into the chamber 5 are made in the lateral wall4 of the flame tube, which openings 7 are closed off when the transversemovable base 3 is in its first position and freed when it is occupyingits second position. Thus, the movable base 3 makes it possible for thecombustion chamber 5 to be separated from and placed in communicationwith the incoming mixture in the manner of the prior art valves,controlling the supply device.

As the two figures show, the movement of the transverse base 3 betweenits two positions is, in this preferred embodiment, of the sliding typealong the longitudinal axis A, but it could be of the rotary, or evenhelical, type. Thus, to mark the first position of the sliding base 3,an internal annular shoulder 8 is provided in the lateral wall 4 of thetube, with the result that the base is applied against this shoulder 8by the chamfered edges thereof during each operating cycle of theengine, thereby defining its “top dead center”. Moreover, to maintainthe sliding base 3 in this first position during the detonation phase ofthe engine, releasable locking means 9 are provided in order totemporarily couple the sliding transverse base 3 with the tube 4.

In the embodiment illustrated, the transverse base 3 takes thestructural form of a piston 10 composed, as is usual, of a transversewall 11 facing the combustion chamber and of a lateral skirt 12 whichcooperates, with a close fit, with the lateral wall 4 of the tube 2. Inthis way, as shown in FIG. 1, the lateral skirt 12 of the piston closesoff the admission or supply openings 7 for the combustible mixture,which openings are made in the tube 2 adjacently to the internal annularshoulder 8.

Situated inside the piston 10 is a cylindrical internal block or body 14which cooperates with the lateral skirt 12 of the piston and has one end15 which is conical so that it can engage in a corresponding axial hole16 made in the center of the transverse wall 11 of the piston and thusemerge in the combustion chamber 5. It will therefore be understood thatthis block is axially movable with respect to the piston under theaction of the detonation gases. Moreover, as shown in FIG. 1, lockingrollers or balls 17 are accommodated in radial passages 18 of thelateral skirt of the piston and partly engage, under the action of aconical shoulder 19 forming a ramp and provided at the periphery of theblock 14, in reception housings 20 made correspondingly in the lateralwall 4 of the tube 2. Two rollers 17 are represented in FIG. 1 but thenumber thereof could be different. The assembly formed by the internalblock 14 and the rollers 17 defines the locking means 9 for immobilizingthe piston 10, that is to say the transverse base 3, in its firstposition.

In addition, elastic return means 21 are provided between the transversemovable base 3 and the tube 2, on the opposite side from the chamber 5in order to spontaneously return said base from its second position(FIG. 2) toward its first, locked position (FIG. 1). For example, thesemeans are simply defined by a compression spring 22 arranged between theend 23 of the block, this end being opposed to the conical end 15, and atransverse support 24 provided in the tube 2. In the conventionalmanner, a guide rod 25 for the spring, emanating from the end 23 of saidblock, may be associated with said spring.

The operating cycle of such a pulsed detonation engine described aboveis as follows.

First of all, it is assumed that the engine I is in the configurationillustrated in FIG. 1 in which the transverse movable base 3 is in itsfirst position, that is to say:

-   -   is bearing against the internal annular shoulder 8 of the tube        2, under the action of the spring 22, and provides the        combustion chamber 5 with sealing through the cooperation of the        chamfered edges of the piston 10 and of the shoulder 8;    -   closes off the admission openings 7 of the tube by way of the        lateral skirt 12 of the piston 10, with the result that the        combustion chamber 5 is separated from the incoming mixture        obtained from the supply device 6; and    -   is locked in this position by the locking rollers 17 passing        partially through its lateral skirt 12 and engaged in the        reception housings 20 of the tube, through the action of the        conical ramp 19 of the block 14, this block being pushed by the        spring 22 and having its end 15 close off the hole 16.

When the detonation of the compressed combustible mixture in the chamber5 takes place, via an ignition device which will be described inrelation to FIG. 3, the pressure increases greatly in the chamber, butthe piston 10 of the base 3, forming the thrust wall, is locked inposition by the locking rollers 17 and is therefore unable to retreat.By contrast, the detonation gases are in contact with the conical end 15of the internal block 14, which end emerges in the chamber 5 through thecentral hole 16 of the transverse wall 11 of the piston, and these gasesact on the block which, as a result of the pressure generated, retreatsand starts to compress the spring 22. During its axial retreatingmovement, the locking rollers 17 follow the conical ramp 19 of the block14 and thus leave the housings 20 of the flame tube 2 so as to beaccommodated in the radial passages 18 of the piston.

The pressure in the combustion chamber 5 is provisionally droppedthrough the effect of the rear expansion of the detonation products and,since the movable base 3 is no longer locked, this space can thereforeretreat freely, together with the internal block 14, to the left in FIG.1 against the action of the spring through the effect of the residualoverpressure prevailing in the chamber. Simultaneously, the lateralskirt 12 of the piston 10 uncovers the admission openings 7 of the tube2 and the movable base 3 then reaches its second position illustrated inFIG. 2, compressing the spring 22 arranged between the support 24 forthe tube and the end 23 of the block.

The admission openings 7 of the flame tube 2 are entirely freed duringthe depression phase caused by the overexpansion of the detonationproducts. Moreover, an auto-suction phenomenon consequently makes itpossible for the combustion chamber 5 of the engine to be autonomouslyfilled with fuel/oxidizer mixture from the supply device.

Then, under the action of the compression spring 22, the internal block14 and the movable piston 10 are returned toward the chamber, the pistonclosing off the admission openings 7 and butting axially against theshoulder 8 of the tube, while the locking rollers 17, under the actionof the conical ramp 19, re-engage in the housings 20 of the tube,thereby immobilizing the base 3 in its first position.

A new operating cycle for the engine I can begin.

In the embodiment II of FIGS. 3, 4 and 5, the transverse immovable base3 of the flame tube 2 is mounted rotationally on a piston 40 arranged inthis tube, for example by means of an elastically loaded axial shaft 41(in a manner which is known but has not been represented). At itsperiphery, the transverse movable base 3 is provided with locking tenons42 which are able to cooperate, in said first position (FIG. 4), withlocking housings 43 made in the thickness of said flame tube 2. Eachlocking housing 43 is in the shape of a L with an axial branch 43A and atransverse branch 43T. Each transverse branch 43T is in communicationwith the combustion chamber 5 through a duct 44, which emerges at 45 onthe combustion chamber side.

The operating sequence for the engine II of FIGS. 3 to 5 is as follows:

-   -   since the assembly of the transverse movable base 3 and the        piston 40 are in the first position (FIG. 4), and the locking        tenons 42 bear in the transverse branches 43T of the locking        housings 43 under the action of the elastic load on said axial        shaft 41 and the supply openings 7 are closed off;    -   when the detonation of the combustible charge present in the        combustion chamber 5 is initiated, the pressure increases        greatly in said chamber, but the transverse movable base 3 and        the piston 40 are immobilized by the locking tenons 42 and are        unable to retreat;    -   however, when the detonation sweeping over the combustion        chamber 5 reaches the height of the orifices 45 of the ducts 44,        a portion of the pressurized gases is captured and directed        toward the locking housings 43;    -   under the action of the overpressure in said locking housings        43, the tenons 42 are driven laterally out of the transverse        branches 43T against the action of the elastic load on the axial        shaft 41, with the result that the transverse movable base 3        rotates with respect to the piston 40 and unlocks the latter;    -   the assembly of the transverse movable base 3 and the piston 40        is therefore able to retreat freely through the effect of the        residual overpressure so as to assume said second position and        expose the supply openings 7, said tenons 42 following the axial        branches 43A of the housings 43;    -   said supply openings 7 are completely open during the depression        phase caused by the overexpansion of the detonation products,        the self-suction phenomenon making it possible for the        combustion chamber 5 to be filled autonomously with        fuel/oxidizer mixture;    -   under the action of the return spring 21 (not shown in FIGS. 3        to 5), the assembly of the movable base 3 and the piston 40 is        returned toward the front, the locking tenons 42 follow the        axial branches 43A of the housings 43 and, once they have come        up against the front stop, penetrate the transverse branches 43        under the action of the elastic load on the axial shaft 41,        causing the base 3 to rotate in a limited manner.

The engine II is therefore once more in its first position, ready for anew cycle.

In addition to the aforementioned advantages provided by the movablebase (combustion chamber/incoming air supply and uncoupling), thereciprocating movement of the thrust wall may also be exploited toproduce the energy which can be used to ignite the combustible load orto partly cover the electrical requirements of the motorized appliance.

Such is particularly the case with the ignition device 30 represented inFIG. 3, which, via means 31, 32, 33, 34 uses the reciprocating movementof the transverse movable base 3 to cyclically ignite the combustiblecharge.

In the embodiment illustrated, this device 30 is of the piezoelectrictype but it could be in the form of an induction coil or the like.Structurally, the means of the device comprise a movable weight 31, aretaining device 32 such as, in this example, an electromagnet, anelastic element 33 and a piezoelectric member 34.

The weight 31 is provided with a lug 35 so that it can be connected tothe movable base 3 (not shown), and it is arranged between theelectromagnet 32 and the piezoelectric member 34 to allow it to move ina reciprocating manner parallel to the axis A between two respectivepositions.

The first position of the weight 31 corresponds to the lower half-viewof FIG. 3 in which the weight 31, fed in by the retreating movement ofthe movable base via the lug 35, is primed and connected to theelectromagnet 32 by virtue of the supply current circulating in thelatter. In this primed position in which the movable base is in itssecond position (FIG. 2), the elastic element 33, such as a compressionspring, situated between the electromagnet and the weight, is compressedand the weight is moved away from the piezoelectric member. In thisexample, the retaining device 32 for the weight is of the electricaltype but it could be of the mechanical type.

The second position of the weight 31 corresponds to the upper half-viewof FIG. 3 in which the weight is released from the retaining device andstrikes against the crystal of the piezoelectric member 34 as a resultof the supply current of the electromagnet 32 being cut off and of theaction of the elastic element 33. Its contact with the piezoelectricdevice 34 generates a high-voltage current used for igniting the engine,that is to say for igniting the combustible charge, when the movablebase 3 is in its first position (FIG. 1).

Furthermore, the Applicant has found that the movable thrust wall alsomakes it possible to have better control over the thrust by smoothingthe pulse-like character of the detonation and by attenuating thevibratory environment likely to be generated by such an engine, whichcan only facilitate the integration of this type of engine inaeronautical airframes.

1. A pulsed detonation engine supplied cyclically with a combustible charge fed into the combustion chamber (5) of a flame tube (2) with a transverse base (3) by a supply device (6), wherein: said transverse base (3) of the flame tube (2) is mounted so that it can move with respect to the latter in order to be able to occupy two boundary positions, a first position corresponding to the detonation phase of the combustible charge in the combustion chamber (5) of said tube and a second position corresponding to the phase wherein the combustible charge is supplied to said chamber; at least one supply opening (7) for said combustible charge is provided in the lateral wall (4) of said tube, this opening being closed off and separated from said combustion chamber (5) by said movable base (3) when the latter is occupying its first position and being in fluid communication with said chamber (5) when said movable base (3) is occupying its second position; and in said first position, said transverse movable base (3) is secured to said tube (2) by releasable locking means (9; 42, 43).
 2. The engine as claimed in claim 1, wherein said transverse movable base (3) slides with respect to said tube (2) between the first and second positions.
 3. The engine as claimed in claim 1, wherein said transverse movable base (3) rotates with respect to said tube (2) between the first and second positions.
 4. The engine as claimed in claim 1, wherein said transverse movable base (3) takes the form of a piston (10) with a transverse wall (11) facing said chamber and with a lateral skirt (12) cooperating with the wall (4) of said tube in order to close off said supply opening (7) in the first position of said base, and said releasable locking means (9) comprise an internal block (14) housed in said piston (10) in a sliding manner and passing through its transverse wall (11) so as to emerge in said combustion chamber (5), and also at least one locking roller (17) subjected to the movement of said block and being able to pass radially through the lateral skirt (12) of said piston in order to engage in a reception housing (20) of said tube and to immobilize said base.
 5. The engine as claimed in claim 1, wherein said transverse movable base (3) is mounted rotationally on a piston (40) arranged in said flame tube (2) and is provided with peripheral locking tenons (42) which are able to cooperate, in said first position, with locking are housings (43) which are made in said flame tube and are in communication with said combustion chamber and (5), through the effect of a detonation, said transverse movable base (3) rotates with respect to said piston (40), inhibiting the cooperation of the locking tenons (42) and the locking housings (43) and enabling said piston (40) to assume said second position.
 6. The engine as claimed claim 1, wherein an internal stop (8) is provided in said tube (2) in order to mark the first position of said movable base.
 7. The engine as claimed in claim 6, wherein said internal stop takes the form of an internal annular shoulder (8) emanating from the lateral wall (4) of said tube (2) and against which the piston of said movable base (3) is applied in its first position.
 8. The engine as claimed in claim 1, wherein elastic return means (21) are provided in said tube (2) in order to return said movable base (3) from its second position toward its first position.
 9. The engine as claimed in claim 8, wherein said elastic return means (21) comprise at least one spring (22) acting on the block of said movable body (3).
 10. The engine as claimed in claim 6, wherein said lateral supply opening (7) is disposed adjacently to said internal stop (8).
 11. The engine as claimed in claim 1, of the type comprising an ignition device, wherein said ignition device (30) comprises means (31, 32, 33, 34) for using the reciprocating movement of said transverse movable base (3) and cyclically igniting the combustible charge.
 12. The engine as claimed in claim 11, wherein said ignition device (30) is of the piezoelectric type and comprises a movable weight (31) connected to said transverse movable base, a retaining device (32) which is able to maintain said weight in the primed position, an elastic element (33) for returning said weight to the percussion position subsequent to the release of said retaining device, and a piezoelectric member (34) generating an electrical current in order to ignite said combustible charge when said weight comes into the percussion position. 